This invention pertains generally to chemical reactors and more particularly to a process and apparatus for carrying out chemical reactions in the glow discharge region of a plasma.
In plasma reactors of the type to which the invention pertains, a reagent gas is excited with radio frequency energy in a reaction chamber. Such reactors are utilized in a wide variety of applications, including chemical etching of various metals such as aluminum.
It has been observed that in the plasma reactors of the prior art, the ionizing current tends to be concentrated toward the walls of the chamber in a manner analogous to the electrical skin effect, or tendency of high frequency currents to flow near the surfaces of metal conductors. In a plasma reactor, the ionized and excited species which form the plasma are created primarily in the region where the current flows. In this same region, visible light commonly known as a glow discharge is produced by the decay of various species in electronically excited states. The life of some excited species is apparently so short that these species do not have time to diffuse out of the region where the current is concentrated. It has been found that certain reactions, such as aluminum etching, can only be carried out in the glow discharge region, and when the glow discharge occurs only near the walls of the reactor, only a small part of the chamber can be utilized.